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Perennial Ragweed

Perennial ragweed1

Perennial ragweed2

Chinese mugwort leaves

Chinese mugwort flowers



family

Asteraceae

status

Perennial ragweed (Ambrosia psilostachya) is listed as noxious in category 4 in Bega Valley LCA. This is actually based on a misidentification of Chinese mugwort (Artemisia verlotiorum), a very similar looking plant which is naturalised along the Bega River in that LCA.

Description

Perennial ragweed is a perennial herb 30-150cm high which grows in dense colonies arising off a system of rhizomes. Stems are branched in the flowering region. Leaves are deeply divided, grey-green, hairy or rough to the touch, aromatic. Individual flowers are small and grouped into terminal spikes. Chinese mugwort is very similar in size and habits, also with deeply lobed leaves, of which the top surface is grey-green and the underside white.

Preferred habitat and impacts

Chinese mugwort is naturalised on sandy soils near Bega, mostly on the banks and in-stream islands of the Bega River. Plants die back to the roots over winter but grow rapidly in spring and summer and flower in late summer. Perennial ragweed does not occur in the region. Its habitat is semi-arid grasslands, roadsides and waste ground on the western slopes and plains.

Chinese mugwort is not palatable to stock and by forming dense stands which exclude all other plants can reduce carrying capacity.

Dispersal

Seed is spread by wind and in water. The plants spread locally by rhizomes. Most long-distance spread of Chinese mugwort in the Bega area is by removal of sand containing seed or rhizome fragments from the river for top-dressing roads and tracks or for building.

Look-alikes

The plants are reminiscent of chrysanthemum, in the height and leaf form, but the flowers are inconspicuous.  There are a number of similar species called ragweeds and distinguishing between them may require expert assistance.

Control

Cultivation is unlikely to be effective because of the extensive rhizome system. Herbicides would be the only possible means of controlling large infestations, but the proximity to water of most infestations restrict the type of herbicides which could be used. Glyphosate, which is registered for use near water, is non-selective and by killing all plants it contacts, runs the risk of creating bare ground and destabilising the river banks. Early detection and removal of seedlings is the best treatment in new areas of infestation.